This is a weird one, but hopefully someone can chime in and confirm I'm not crazy.
About a year ago I bought a pair of Shure SE425s to replace my worn-out SE210s. For the 210's I had a set of custom earmolds made (by ListenHear, which is no longer in business) and everything fit and sounded great. When I got the 425s I started out by using the medium grey flex sleeves, which from past experience I knew were comfortable and long-lasting, but found that my 425s sounded worse than the 210s they replaced. While the low end was definitely better, the high end was a bit muffled and undetailed, to the point where I became convinced that my earphones were defective. To be sure I stuck the triple-flange sleeves on them, and they sounded the same, so off to Shure they went for a warranty replacement.
The replacement 425s came with the black medium foam sleeves already attached, which I left on for my first listen of them. Everything sounded fantastic! The highs were exactly as I'd expected them to sound originally, so I figured my original pair were indeed defective somehow and that the whole problem was resolved. That is, until I put the grey flex sleeves back on...at which point they sounded horrible again.
After taking a close look at all of the sleeves Shure includes, the major difference I can discern is the size of the opening that points into the ear canal. On the black foamies, the opening is significantly larger than on the grey flex or triple-flange. This is the only thing I can think of that might affect the high-frequency response.
Has anyone else noticed this with their Shure IEMs? I'm not a fan of the black foamies since they tend to wear out more quickly and have the tendency to get stuck to the earphone nozzles (which requires a visit to the freezer and some careful prying to remove). My old custom molds will actually fit on the 425s, but they no longer fit into my ears properly since I've lost weight since they were made. Any recommendations on alternate sleeves I can try that are like the grey flex sleeves? Or, are there any recommended manufacturers of custom molds (I'm not interested in a reshell) other than Sensaphonics? (Or, does anyone know of Starkey Labs, the former parent of ListenHear, still offers custom molds?)